They all meant the same. In Scala 2.8 this has changed.
The difference is that the package clause

package org.myproject.tests

now only brings the members of the org.myproject.tests in scope, but
not the members of the two outer packages org.myproject and org.
If you want to have the members of both tests and org.myproject
in scope you need to use the two nested package clauses above, or else the
chained equivalent:

package org.myproject // myproject members are visible, but not org members